1. Field of the Invention
The present invention generally relates to an ion implanter and an ion implant method, and more particularly, to implant a wafer by using both the wafer movement and the aperture movement, where the aperture is configured to filter an ion beam before wafer being implanted. Optionally, the size/shape of the aperture may be similar to that of a traditional spot beam when the ion beam is a ribbon ion beam, the incidental angle between the wafer and the ion beam may be fixed, and the aperture may be significantly smaller than the cross-section of the ion beam.
2. Description of Related Art
Ion implantation is a popular and important processing step performed during semiconductor manufacture, so that a wafer is implanted by an ion beam. The ion beam may be a spot ion beam or a ribbon ion beam, and the implanted wafer has a special dose distribution, no matter a uniform dose distribution or a non-uniform dose distribution (such as a wafer has different doped regions having different doses, even having different shapes/sizes).
FIG. 1A is a simplified diagram of a traditional ion implanter 100. The traditional implanter 100 includes an ion source 110 and an analyze magnet 120. The ion source 110 is used to generate an ion beam, and the analyze magnet 120 are used to filtered undesired ions out the ion beam before implanting the ion beam into the wafer 10. As usual, although not particularly illustrated, some electrodes and some magnets are positioned between the analyze magnet 120 and the wafer 10 to accelerate/decelerate the ion beam, deform/shape the ion beam, and/or to modify other properties of the ion beam before the wafer being implanted.
FIG. 1B shows a top view of the wafer 10 depicted in FIG. 1A. Several popular ion implant methods exist for property implanting the ion beam 20 into the wafer 10. If the wafer 10 is fixed, the ion beam 20 can be moved on a plane defined by the X-axis and the Y-axis. If the ion beam 20 is fixed, the wafer 10 can be moved on the plane defined by the X-axis and the Y-axis. Also, the ion beam 20 and the wafer 10 can be moved respectively along different directions on the plane defined by the X-axis and the Y-axis simultaneously.
The concept “fixed the ion beam” means that the ion beam is directed along a fixed ion beam path without scanning around the space close to the wafer, i.e., at least partial ion beam path proximate to the wafer is fixed. Under such situation, the wafer is moved across the ion beam, even also is moved along the ion beam, to ensure proper implantation. Depending on the required dose distribution over the wafer, both the scan path and the scan speed are adjustable parameters. Also, depending on the required dose distribution over the wafer, the ribbon ion beam and the spot ion beam may be flexibly used. Besides, depending on whether a spot ion beam or a ribbon ion beam is used, the scan path and the scan speed usually are flexibly adjusted.
However, when the size of the wafer is increased, the wafer must be correspondingly moved a longer distance so that the wafer is properly implanted by the ion beam, also the weight of the wafer is correspondingly increased. For example, when the beam height of the ion beam is fixed at H and the wafer thickness is fixed, to ensure uniform implantation over whole the wafer, the required minimum movement distance of a wafer with diameter R along the beam height direction is the difference between R and H, R−H, but the required movement distance of a larger wafer with diameter 2R along the beam height direction is the difference between 2R and H, i.e. 2R−H. Clearly, the former has to move a wafer and its support structure having a weight W along a distance (R−H), but the latter has to move a wafer and its support structure having a larger weight ˜4W a larger distance (2R−H). Undoubtedly, the required energy to move the wafer is increased, even the hardware cost and the operation complexity of the mechanism for moving the wafer are correspondingly increased. Such disadvantages are more serious for the next generation that the wafer diameter is about 450 mm (or viewed as about 18 inches).
Of course, a solution is to increase the beam height of the ion beam, especially the size of the uniform portion of the ion beam. Thus, the required movement distance of the wafer can be decreased, even may be zero if the beam height is larger than the wafer diameter. Nevertheless, to increase the beam height of ion beam usually means higher hardware cost and higher operation complexity of the ion implanter, also may decrease the uniformity of the ion beam. These disadvantages are more serious for the next generation that the wafer diameter is about 450 mm (or viewed as about 18 inches). Besides, for some special cases, such as the wafer has different dose regions having individual doses even different shapes/sizes/doping-depth, a spot ion beam or a shorter ribbon ion beam may be convenient and useful.
Another solution is moving the wafer only along the beam width direction but moving the ion beam along the beam height direction, and one another solution is fixing the wafer but moving the ion beam along both the beam height direction and the beam width direction. Thus, the disadvantages described previously may be avoided because the wafer is not moved along the beam height direction now. Nevertheless, when the ion beam is swung over the wafer, the incident angle between the implanted ion beam and the surface of the wafer varies among different portions of the wafer. In such situation, it is difficult to precisely control the properties of the implantation on the wafer, also the distribution of implanted ions inside the wafer will be non-uniform over different portions of the wafer. Hence, even the moving speed of the ion beam is uniformly over the wafer and the beam current of the ion beam is continuously stable during the period of scanning the ion beam over the wafer, the implantation result over the wafer is still not precisely controlled and non-uniform. As usual, one or more additional step(s) and/or additional device(s) are required to precisely control the implantation on the wafer. For example, a mask having an aperture is moved with the ion beam simultaneously, where the shape and the size of the aperture is essentially equal to that of a projected area of the ion beam on the wafer when the ion beam is vertically implanted into the wafer. Thus, when the ion beam is not vertically implanted into the wafer, the edge portion of the ion beam is filtered out by the aperture and only the center portion of the ion beam is implanted to the wafer. In addition, to keep the center portion of the ion beam fixed for different incident angles, it is an option to use a mask having an adjustable aperture. Nevertheless, the usage of the mask unavoidably increases the hardware cost and the operation complexity, especially the usage of the mask having adjustable aperture.
According to the above discussions, there is a need to propose a novel ion implanter and a novel ion implant method to implant a wafer.